The present invention relates generally to dynamic information storage and retrieval units, and more particularly to precise and efficient storage of timing and control information in the media structure of such units. The invention may be used on storage units employing rotating disks of magnetic, optical, or other media types. The inventor anticipates that the primary initial application of the present invention will be in the creation of clock information for use in writing servo tracks on magnetic media during assembly of rotating rigid disk storage units such as computer hard drives.
Dynamic data storage and retrieval has become of very great importance in our increasingly information based society. In both our work and enjoyment we typically use computers or computerized systems which read and write data on various storage media contained in removable or installed (xe2x80x9cfixedxe2x80x9d) storage units. Users of such storage systems typically want to handle a lot of data both efficiently and safely, and at low cost. Today a ubiquitous example off a storage unit generally meeting these criteria is the hard disk drive (hereinafter xe2x80x9chard drivexe2x80x9d). Worldwide some 200,000 hard drives are manufactured every day.
Hard drives consist of one or more spindle mounted disks which have magnetic media on one or, more typically, both major sides. The terms xe2x80x9cdisk packxe2x80x9d and xe2x80x9cdisk platterxe2x80x9d (or even simply xe2x80x9cplattersxe2x80x9d) are widely used terms for an assembly of such disks. A motor is provided to rotate the disk assembly and arms bearing read/write heads (xe2x80x9cR/W headxe2x80x9d) are positioned pivotally or linearly above the media to magnetically write or read data into and from the media (an: assembly of such arms and R/W heads is commonly termed a xe2x80x9chead stackxe2x80x9d). To efficiently and reliably later access user data a scheme of concentric tracks and sectors within those tracks are defined during hard drive manufacturing using a process called xe2x80x9cservo track writing.xe2x80x9d This process places servo data in a proprietary coding in the disk media called a xe2x80x9cservo pattern.xe2x80x9d Data storage density in hard drives thus very much depends upon how densely such tracks and sectors can be defined and reliably used. Hard drives coming available today have track densities as high as 10,000 tracks per inch (TPI), and manufactures hope to obtain 20,000 TPI in the next 3-5 years.
Accurately manufacturing hard drives economically and in large quantity is not easy. For example, due to the limitations of mechanical tolerances inherent to manufacturing, the actual speed of rotation of disk platters is not exactly the same in every unit produced. If a hard drive is designed to optimally store n sectors of data in each track, platter revolution speeds that cause nxe2x88x922 or n+3/4 sectors to be written can cause unexpected and even disastrous results (often at some later point outside of the closely controlled manufacturing environment). Such variation can be termed xe2x80x9csector-inconsistency error.xe2x80x9d Of course, the hard drive can be designed with tolerances to accommodate an expected degree of sector-inconsistency error, but that seriously undercuts the goal of achieving a high data-per-track storage density.
Further, similarly due to manufacturing limitations, the disk platter rotation is never perfectly circular. If this imperfection is severe enough it can even cause the coding to be mistakenly written to a different data zone, called an xe2x80x9coff-track error.xe2x80x9d One solution for this is to allow the physical width of the track to be such that the possibility of off-track error becomes negligible, but this reduces the TPI and seriously undercuts the goal of achieving a high data-per-platter storage density.
To address these problems, and to a lessor extent others as well, the industry has turned to putting clock information into hard drives prior to writing the servo information. FIG. 1 (background art) is a simplified depiction of this (as noted above, actual hard drives are typically much more complex than this, but this simplification illustrates the necessary principles of operation). Within a workpiece hard drive 1 (shown only in pertinent detail) a media disk 2 rotates on a hub 3. A clock arm 4 bearing a clock head 5 is then introduced and a clock pattern, i.e., a clock track 6, is written at the outer periphery of the media disk 2. Once the clock track 6 is written, the clock head 5 is used to read it back and the regular R/W head 7 of the hard drive 1 is used in a synchronized manner to write the desired servo pattern into the media disk 2.
A servo pattern may also be complex. It may be embedded throughout the data storage area on the media disks or placed on a single media surface dedicated to it (a servo pattern is intentionally not shown in any of the drawings herein because of the confusion which doing so might cause; also, an older wedge servo system has been used in hard drives but is now obsolete). However, it should be noted that in a hard drive only one clock track is needed.
The process of writing the clock pattern and the servo pattern is quite complex, and requires extremely precise timing, measurement, and positioning. First the clock pattern must be written. The platter of media disks is brought up to its operating speed, which commonly will be 5,400, 7,200, or even 10,000 rpm, and an initial clock pattern is written using the clock head. However, this initial pattern usually has one clock increment which is less than or greater than the others (e.g., nxe2x88x921/2 or n+3/4), and in extreme cases the number of clock increments may even be less than or greater than desired (e.g., nxe2x88x921 or n+2). Therefore, to create consistent clock information, the initial clock pattern is read back as a measurement of actual hard drive conditions, calculations are performed to determine what is needed to obtain a clock pattern with the desired number of consistent increments, and based upon this a final clock pattern is written.
Next, the media disks are maintained at operating speed and the clock head, which is still introduced to the hard drive, is used to read back the clock pattern while the R/W heads are used to write the servo pattern. Feedback from the clock pattern is used to write the servo pattern in a manner such that data will later be stored in a desired and consistent number of sectors. Concurrently, this feedback from the clock pattern is also used to insure that servo track writing accurately follows the rotation of the disk and that the R/W heads are adjusted to write the servo pattern in a more perfect circle. During this process feedback techniques are used to measure and position the actual R/W heads very accurately during the actual servo pattern writing. Today, laser interferometry generally is used for this but some manufacturers also employ optical encoders.
Unfortunately, there are a number of problems, compromises and lost efficiencies associated with the above-described use of a magnetic disk based clock pattern. It should be appreciated that the clock head and clock pattern are used only in hard drive assembly. Obviously, if the area used by the clock pattern, i.e., the clock track, could otherwise be used for data storage this would increase the storage capacity of the hard drive. Further, because the clock head and the associated electronics for it are expensive and cumbersome, hard drive manufacturers understandably prefer to make these part of the external manufacturing apparatus, rather than include instances of them in every hard drive being produced. But this means that the clock head must specially be introduced into the hard drive during assembly, slowing the assembly process, and perhaps more importantly putting tooling and product in harms way (those familiar with the art of magnetic recording will readily appreciate that for the clock head to write and read the media surface it must be brought very close, typically on the order of 6 micro-inches).
However, to the inventor, based upon his own years as a provider of equipment to many of the largest hard drive manufacturers, the biggest cause for concern is the level of cleanliness which must be maintained during assembly of many storage units using current techniques. As touched upon above, head to media clearances are very small and the relative speed between these when in operation is extremely high. Any contamination that enters the confines of such a storage unit can have catastrophic consequences, which hopefully will turn up early before the manufacturer performs final tests on the unit, but which all to often instead turn up later and cause the loss of an ultimate user""s precious data.
Among computer users the term xe2x80x9chead crashxe2x80x9d is all too well known, it means the catastrophic loss of data by damage to the media surface or even loss of the entire hard drive due to the disk platter and head stack literally jamming. The present inventor frequently has removed part of a hard drive housing to display aspects of working hard drive operation. It has been his observation that in a few hours, maybe a day, some media degradation occurs, as evidenced by the drive having seek problems. Then within a day, or typically at most a week, the hard drive completely jams up. To additionally understand this phenomena in hard drives it should be appreciated that static charged a particles are readily attracted to and build up on magnetically charged media surfaces.
Hard drive manufacturers also dread head crashes, because dissatisfied customers often will never buy a product from them again. (This is not at all an exaggeration. Among repair personnel and computers users prejudices are easily built from a few bad experiences, and then often vehemently verbalized to others, which undercuts the market goodwill of the often coincidental particular manufacture.)
To prevent contamination, manufactures resort to using clean rooms for assembly. In hard drive manufacturing the current standard for cleanliness is xe2x80x9cClass 10,xe2x80x9d and the cost of a clean room to achieve this is very high. Based upon the inventor""s own experience and extensive conversations with experts in the field, this exceeds U.S. $10,000,000 per hard drive manufacturer today. Further, even with class 10 clean room facilities, rigorous and tedious process control is needed to ensure that no contamination is introduced.
Work has been done in the industry to try and eliminate the need for such cleanliness and the need for clean rooms, but until the present invention this has not become possible. For example, the present inventor is the inventor also of U.S. Pat. No. 5,315,372 for a xe2x80x9cNon-Contact Servo Track Writing Apparatus Having Read/Head Arm And Reference Arm,xe2x80x9d and a number of currently pending patent applications for non-invasive servo pattern writing. Using such non-invasive techniques for servo pattern writing has reduced but not eliminated the need to have storage units open during assembly, because there must still be at least one open portal for the clock head access during clock pattern writing.
Accordingly, what is needed for manufacturing of some important classes of information storage units today are apparatus and methods to better write clock patterns. Such solutions should very preferably work on sealed storage units; and it is highly desirable that they not introduce any new instances of, or even better still, reduce or eliminate existing problems, compromises, or lost efficiencies related to the manufacturer of such information storage units.
Accordingly, it is an object of the present invention to provide servo pattern writing techniques usable on hermetically sealed information storage units.
Another object of the invention is to eliminate the need to dedicate a portion of the storage media in information storage units to storage of a seldom used clock pattern.
Another object of the invention is to modify storage unit assembly techniques to minimize or even eliminate providing and maintaining clean assembly environments.
And, another object of the invention is to modify storage unit assembly techniques so that they are more flexible in ordering the various steps required.
Briefly, a first preferred embodiment of the present invention is an apparatus for inscribing a clock pattern in the platter of an information storage unit using rotating disk shaped storage media. The apparatus includes a laser system to emit a light beam used to mark the platter in a manner which is later optically detectable. A directing assembly is provided to direct the light beam to a target position in an annulus (a ring) defined somewhere on the platter and centered about its axis of rotation. A controller is provided for controlling both the laser system and the directing assembly so that a desired number of clock marks are inscribed in the annulus, all consistently spaced apart, to form an optically created and detectable clock pattern.
Briefly, a second preferred embodiment of the present invention is a method for inscribing a clock pattern in the platter of an information storage unit using rotating disk shaped storage media. An annulus is specified somewhere on the platter which is nominally centered about its axis of rotation. Then a separation value is calculated equal to the circumference of the annulus divided by the number of the clock marks desired in the clock pattern (an integer value). Optically detectable clock marks are then inscribed in the annulus such that each adjacent pair is consistently spaced the same distance apart by the separation value and their total number equals the desired number of clock marks in the clock pattern.
Briefly, a third preferred embodiment of the present invention is a method for writing a servo pattern in an information storage unit having a rotating platter of disk shaped storage media. The platter is provided with a clock pattern already inscribed in it, and is assembled into the storage unit. The platter is then rotated within the storage unit. The clock pattern is optically detected, i.e., read back. And the servo pattern is written into the storage media in relation to the clock pattern.
Briefly, a forth preferred embodiment of the present invention is a different method for writing a servo pattern in an information storage unit having a rotating platter of disk shaped storage media. The storage unit is assembled, and the platter is rotated in it. Then a clock pattern is inscribed into the platter. This clock pattern is detected optically, i.e., read back. And the servo pattern is written into the storage media in relation to the clock pattern.
Briefly, a fifth preferred embodiment of the present invention is a different method for writing a servo pattern in an information storage unit having a rotating platter of disk shaped storage media. The platter is provided with a clock pattern already inscribed in it. During assembly of the storage unit, a window is installed and the storage unit is sealed hermetically. The clock pattern is then detected optically through the window, and used for servo pattern writing.
Briefly, a sixth preferred embodiment of the present invention is a different method for writing a servo pattern in an information storage unit having a rotating platter of disk shaped storage media. During assembly of the storage unit, a window is installed and the storage unit is sealed hermetically. Then a clock pattern is inscribed in the platter optically through the window. The clock pattern is then detected optically through the window, and used for servo pattern writing.
Briefly, a seventh preferred embodiment of the present invention is an apparatus for writing a servo pattern in an information storage unit having a rotating platter of disk shaped storage media. A measuring system is provided for measuring angular position of the platter while the storage unit is hermetically sealed. A writing system is provided for writing the servo pattern into the storage unit in relationship to what the measuring system measures.
An advantage of the present invention, since the workpiece storage unit may be sealed, is that a less stringent manufacturing environment may be used. For example, when the workpieces are conventional hard drives the process of servo pattern writing can now be entirely carried out without using expensive, and notoriously difficult to operate and maintain clean room environments.
Another advantage of the invention, since all sensing may be performed optically, is that much greater sensing distances can be employed, all reliably and speedily, and with considerably reduced risk of damage to tooling and the storage units being assembled. For example, while magnetic heads must typically be positioned within a few micro-inches of the media-containing what is being sensed, most optical methods can be used at distances of a few centimeters or even further away. Use of the invention can eliminate the tedious nature of this operation, the risk of the sensing device damaging the media, and concurrently make the results of the sensing operation more reliable.
Another advantage of the invention is the ability to now use optical sensing permits techniques, heretofore not easily used or even possible using prior art techniques like magnetic sensing. For example, optical quadrature sensing, which is widely used with optical media like compact disks, can be employed with some variations of the present invention to enhance the accuracy of sensing the increments in a clock pattern.
Another advantage of the invention is that the clock pattern can be placed anywhere readily accessible on the rotating assembly, on the hub, the periphery of a major disk surface, or even on the outside edge, thereby providing considerable manufacturing flexibility and in some case even freeing up for other use precious media area which would previously have been needed for clock pattern storage.
And another advantage of the invention is that the clock pattern can be written and read, i.e. accessed, from a large range of angles, rather than from merely a normal angle. Thus, while conventional vertical access or even horizontal access can be used, off-normal writing is possible and paired off-normal emitting and sensing devices can also be used for reading. For example, a light beam can be directed from an emitting device to the a clock pattern at a 45 degree angle, and reflected back to a reading device at an incident 45 degree angle.
These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of the best presently known mode of carrying out the invention and the industrial applicability of the preferred embodiment as described herein and as illustrated in the several figures of the drawings.